(1) Field of the Invention
The present invention relates to a semiconductor equipment which includes a semiconductor chip inside a heat pipe, and to a method of manufacturing the semiconductor equipment.
(2) Description of the Related Art
As a material for semiconductor devices, recent years have seen active research and development being carried out on wide bandgap semiconductors such as nitride semiconductors, represented by gallium nitride (GaN), and silicon carbide (SiC).
Wide bandgap semiconductors are characterized in that dielectric breakdown voltage is one digit higher compared to that of Si, and that the on-resistance of a semiconductor device decreases. In particular, since a nitride semiconductor material such as gallium nitride (GaN), together with aluminum nitride (AlN), indium nitride (InN), and so on, allows the production of various mixed crystals, and the creation of a heterojunction which generates a two-dimensional electron gas, it is possible to realize a large-current, low-on-resistance device for high-power use even in a horizontal device where, inside a substrate, current flows in a direction parallel to the main surface of the substrate.
For example, an on-resistance value of 2 mΩcm2 is obtained with a forward breakdown voltage of 600 V, and a high-power GaNFET having a very low on-resistance which is 1/10 or less than that of a conventional high-power MOSFET is realized. On the other hand, when a high-power GaNFET having the same on-resistance with the same forward breakdown voltage as a high-power MOSFET is realized, the chip surface area becomes approximately 1/10 that of the MOSFET, and thus it is possible to realize significant miniaturization of the device for high-power use. However, since heat generation density in this case becomes 10 times that of the MOSFET, the heat-transfer technique for the semiconductor chip becomes very important for a small device made of a nitride semiconductor.
Meanwhile, heat pipes are available as devices which cool by moving a large amount of heat at high speeds. A heat pipe is a metal pipe that is laid out inside a personal computer in order to disperse/eliminate heat generated from a semiconductor and so on. The heat pipe is used in thin laptop computers. Heat is released by placing a coolant in the metal pipe and utilizing the latent heat in the evaporation and condensation of liquid. Gradually transferring heat from a heat source and dispersing the heat allows for a large amount of heat transfer using a small temperature difference.
The heat pipe is structured such that a volatile liquid (working fluid) is enclosed inside a pipe made of a material having high thermal conductivity. The operating principle is as described below. By heating one end of the pipe and cooling the other end, the absorption of latent heat by the vaporization of the working fluid occurs at the hot side, and the release of latent heat through the condensation of the working fluid occurs at the cool side. The working fluid that has liquefied returns to the region where there is little working fluid, through the capillary force of a wick formed inside the pipe. Heat migrates from the high-temperature portion to the low-temperature portion through this cycle, and a high heat-transfer effect can be obtained with an appropriately designed heat pipe compared to a metal radiator (heat sink). Although setting the cold portion at a higher position than the hot portion allows the condensed working fluid to return to the hot portion through gravity, adopting a capillary structure within the pipe allows usage even when there is no difference in elevation. Classification into thermosiphons and heat pipes is based on the presence of a capillary structure (see, for example, Patent Reference 1 (Japanese Patent No. 2583343), Patent Reference 2 (Japanese Unexamined Patent Application Publication No. 11-87586), Patent Reference 3 (Japanese Unexamined Patent Application Publication No. 2009-206369), and Patent Reference 4 (Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-507685).
An example of a heat pipe-type electronic component cooler is shown in FIG. 16 (see Patent Reference 1). An electronic component cooler 20 adopts a heat pipe structure by using a sealed space portion 24 formed in a ceramics package 22. By placing the sealed space portion 24 vertically, the sealed space portion 24 is arranged to be long in the vertical direction. A stepped recess 23 is formed inside the ceramics package 22, and a LSI body 25 in which a semiconductor chip (Si Chip) is packaged is mounted as an electronic component in a rear portion 23b. A wick 26a which is a porous material such as an alumina ceramic material is formed along the surface of the LSI body 25 and the recess 23 in the vicinity thereof. The main portion of the ceramics package 22 has a bowl-shape that opens laterally, a side-lid 22a is secured to lateral portion opening, and the sealed space portion 24 is formed from the side-lid 22a and the recess 23. The side-lid 22a is entirely made of a thin plate of ceramic material which is the same material as the ceramics package 22, and the side-lid 22a is a condensing portion which condenses using the working fluid. Deionized water, Freon, and so on is used as the working fluid.
An example of a cooling structure of a multi-chip module, which uses the heat pipe principle is shown in FIG. 17 (see Patent Reference 2). A multi-chip module is configured of a wiring board 33 mounted with plural LSI cases 32 each having a semiconductor device 31 built into it. A heat-transferring block 35 anchored to the wiring board 33 is attached to the wiring board 33 via flanges 34 so as to cover the LSI cases 32. The heat-transferring block 35, together with the wiring board 33, forms a sealed space encapsulating the LSI cases 32. The cooling mechanism is configured to include: the heat-transferring block 35; a working medium channel including a planar wick 39 and a columnar wick 40 which are provided in the heat-transferring block 35; a cooling fluid 37 which flows inside a coolant channel and cools the heat-transferring block 35; and a working medium 38 sealed inside the sealed space. A perfluorocarbon fluid which is non-corrosive and has insulating properties is used as the working fluid. In order to enhance the seal, a sealing material such as a gasket or an O-ring is used between the flange 34 and the heat-transferring block 35.
An example of a semiconductor equipment including a semiconductor chip inside a heat pipe is shown in FIG. 18 (see Patent Reference 3). A semiconductor chip 51 mounted on a mounting board 55 using a mounting material 53 such as solder. The mounting board 55 includes an insulating layer 55a made of a glass fabric base material epoxy resin (glass epoxy) on the surface-side, an insulating layer 55c made of the same glass epoxy on the underside, and a copper plate 5b disposed therebetween. The semiconductor chip 51 is electrically connected, through bonding wires 52, to a line 55d that is made of copper and formed on the surface-side and the underside of the mounting board 55. The line 55d is connected at the surface-side and the underside via through holes 55e having a wall plane covered by glass epoxy. Then, a wick 57 and working fluid 58 made of water, alcohol, or hydrochlorofluorocarbon, and so on, are injected inside a heat pipe 56. The semiconductor chip 51 and the bonding wires 52 are covered by a passivation film made of bisphenol A epoxy resin.
Furthermore, water, methanol, ethanol, acetone, ammonia, a chlorofluorocarbon (CFC) coolant, a hydrochlorofluorocarbon (HCFC) coolant, a hydrofluorocarbon (HFC) coolant, or a mixed coolant thereof are disclosed as a working fluid used in a stand-alone heat pipe that does not include a semiconductor chip (see Patent Reference 4).